Renal angiomyolipoma is an uncommon be­nign mesenchymal tumor of the kidney. It con­tains fat, smooth muscle, and tortuous blood vessels in varying proportions. First described by Bourneville in 1880, [1] it is often considered to be a hamartoma rather than a malignant neoplasm. Two forms of this tumor are re­cognized clinically; the first is associated with tuberous sclerosis, where the tumor is usually small, multiple, bilateral and has an equal sex distribution. The second form occurs more often in women and is not associated with tuberous sclerosis, and the tumor is often large, single, and unilateral. [2]

A 46-year-old woman presented to her ge­neral practitioner with a two month history of right-sided flank pain, hematuria, and weight loss. She was not diabetic or dyslipidemic and there was no significant past medical or family history. She did not take any medications or had a history of illicit intravenous drug usage.

Physical examination revealed a healthy wo­man. There was no pallor and her blood pres­sure was normal. The serum biochemical pro­file was normal. Routine examination of urine revealed hematuria. Ultrasonography revealed a mass originating from the lower pole of the right kidney.

A preoperative diagnosis of a large solitary right renal tumor was made. At operation, an irregularly shaped tumor consisting mainly of fat was found adherent to the inferior pole of the right kidney. The right ureter was stretched over the upper surface of this tumor. The mass measuring about 8.0 × 5.5 × 5.0 cm and weighing 200 g was excised together with a small rim of normal renal tissue [Figure 1].

Postoperative recovery was uneventful and the patient was discharged in the eighth postoperative day.

Renal angiomyolipoma arises from the me-senchymal elements of the kidney. [3] These tumors consist of a collection of blood vessels, smooth muscle, and mature adipose tissue, although a more aggressive subtype also exists that consists of perivascular epithelioid cells. [4] A total of 80% of angiomyolipoma are associated with tuberous sclerosis. [5] A sporadic and rare form of angiomyolipoma is also found where lesions are usually single, unilateral, and ge­nerally asymptomatic. [6] Renal angiomyolipoma are commonly found as incidental findings on cross-sectional ima­ging (ultrasound, computed tomography or magnetic resonanceimaging). [7] On ultrasound, they usually cast an acoustic shadow and appear homogeneous with high reflectivity due to their high fat content. [5] On CT, angiomyo-lipoma have well-defined margins, with a variable proportion of fat and soft tissue, although the former usually predominates. [4] Histology of angiomyolipoma confirms that they are mainly composed of spindle-shaped smooth muscle cells, and the presence of multiple epithelioid cells is found in the more aggressive form. [8] The majority of patients with renal angiomyolipoma are asymptomatic and it is estimated that over ten million people world­wide have such lesions. [7] In the minority of patients that are symptomatic, the classic "Lenk's triad" of symptoms include flank or abdominal pain, a palpable or tender mass and hematuria [9] Other symptoms may include fever,

vomiting, anemia, renal failure, and hypo-tension. [4] Some angiomyolipoma can grow rapidly, up to 4 cm per year. [10] If greater than 4 cm in diameter, these lesions are associated with an increased risk of aneurysm formation and hence a higher possibility of rupture and hemorrhage. [9] If bleeding presents acutely, it is potentially a life-threatening situation, which may require surgical intervention leading to a possible nephrectomy [11] In all cases, the aim of treatment is to preserve renal function and to prevent hemorrhage. [7]

It is important to recognize the benign nature of these tumors and their characteristic ultra-sonography and CT findings. So that diagnosis of an aggressive neoplasm particularly renal cell carcinoma can be prevented. Most of these tumors are amenable to conservative manage­ment with frequent follow-up. Even when surgical excision is indicated, the kidney itself can often be spared without jeopardizing the patient. Nephrectomy is necessary only when the tumor has replaced the whole kidney or when there is a concomitant renal carcinoma present.